In this photo taken on Wednesday Jan. 4, 2012, women walk past piles of uncollected garbage in Mexico City. Mounds of debris piled up at illegal dumping sites around the city in recent weeks as the metropolis grappled with an avalanche of refuse after closing one of the world's largest landfills. Like other mega-cities around the world, Mexico City is struggling to move from the informal garbage collection systems of the past to modern waste management designed to drastically cut the volume of material that ends up in landfills. (AP Photo/Christian Palma)

MEXICO CITY -- Mounds of debris piled up at illegal dumping sites around the city in recent weeks as the metropolis grappled with an avalanche of refuse after closing one of the world's largest landfills.

Garbage trucks queued up for more than six hours to dump loads at transfer stations, while overstuffed bags and other trash piled up even on the toniest streets over the holidays, when dumps in surrounding Mexico state refused to take the city's trash.

This week, city officials were caught in a front-page photograph dumping tons of trash at the same landfill they claimed to have closed in December, promising a better, greener waste management system for the city of 8.8 million.

"We're seeing a confusion obviously now in the handling of garbage," said Pierre Terras, who coordinates the toxins campaign for Greenpeace Mexico. "You can see it in the streets."

Like other mega-cities around the world, Mexico City is struggling to move from the informal garbage collection systems of the past to modern waste management designed to drastically cut the volume of material that ends up in landfills.

Mexico City officials count some 1,000 illegal dumping sites in a metropolis that generates more than 12,000 tons of trash a day. That includes some trash that is trucked in from neighboring towns in this sprawling metro area of more than 21 million -- one of the world's largest.

The Latin American capitals of Bogota and Buenos Aires, which face similar problems, have committed to Zero Trash, a campaign supported by environmental groups to manufacture reusable goods and materials, recycle and ideally cut the amount of unusable trash to zero. Greenpeace is pushing such a plan for Mexico City.

Everyone agreed that the Bordo Poniente landfill had to close as scheduled on Dec. 31, a move that could mean a drop in greenhouse gas emissions by a minimum of 2 million tons of carbon dioxide annually. Built on a dry lake bed partly to handle the rubble from the devastating 1985 earthquake, it had taken in more than 76 million tons of garbage.

Critics say the city was unprepared, and it wasn't clear why there wasn't a solid alternative waste system in place after earlier plans to build four new garbage processing plants were abandoned.

Meanwhile an interim plan to take refuse to smaller dumps outside the city fell apart almost immediately.

Last week residents of Ixtapaluca in Mexico state blocked a federal highway to prevent Mexico City garbage trucks from unloading at a dump in their neighborhood, while other communities staged similar revolts.

Mexico City has required its residents to separate trash since 2003, but without enforcement or the necessary recycling equipment. Despite public service campaigns, there is no culture for recycling.

Residents still rely on an old collection system in which trucks roam the streets daily, with a garbage man ringing a bell to alert neighbors who come running with their trash cans and bags.

The small amount of recycling is done at the trucks, as garbage workers open bags to separate out glass, plastic and cardboard.

Dumping on the street brings heavy fines. But trash routinely piles up on Mexico City street corners under the cover of night from households where people can't wait around during the day for the trash bell.

"They haven't retrofitted the trucks, they haven't educated the public, they haven't reduced the amount of trash generated. Today we're the same or worse than we were five years ago," said Ramon Ojeda, president of the Mexican Academy for Environmental Rights. "It's a fiasco for the city government."

Secretary of Works and Services Fernando Aboitiz said the city has been preparing for the landfill closure for 14 months and didn't anticipate the reaction to dumping in Mexico state.

Since March, the city has stepped up its trash separation program, negotiating with the sanitation union so that trucks collect food wastes and other organic material separately from recyclable goods.